The present invention relates to a method of treating viral infections, in particular, viral infections that are susceptible to treatment with interferon alpha, comprising the administration of an amount of a polyethylene glycol-interferon alpha conjugate, which amount is effective to treat the viral infection while reducing or eliminating adverse side effects normally associated with administration of interferon alpha. In a preferred embodiment of the invention, administration of a polyethylene glycol having an average molecular weight of 12,000 conjugated to interferon alpha is used to treat chronic hepatitis C.
Interferons are a family of naturally occurring small proteins and glycoproteins produced and secreted by most nucleated cells in response to viral infection as well as other antigenic stimuli. Interferons render cells resistant to viral infection and exhibit a wide variety of actions on cells. They exert their cellular activities by binding to specific membrane receptors on the cell surface. Once bound to the cell membrane, interferons initiate a complex sequence of intracellular events. In vitro studies demonstrated that these include the induction of certain enzymes, suppression of cell proliferation, immunomodulating activities such as enhancement of the phagocytic activity of macrophages and augmentation of the specific cytotoxicity of lymphocytes for target cells, and inhibition of virus replication in virus-infected cells.
Nonimmune interferons, which include both alpha and beta interferons, are known to suppress human immunodeficiency virus (HIV) in both acutely and chronically infected cells. Poli and Fauci, 1992, AIDS Research and Human Retroviruses 8(2): 191-197. Interferons, in particular, alpha interferons, have received considerable attention as therapeutic agents in the treatment of hepatitis C virus (HCV)-related disease due to their antiviral activity. Hoofnagle et al., in: Viral Hepatitis 1981 International Symposium, 1982, Philadelphia, Franklin Institute Press; Hoofnagle et al., 1986, New Eng. J Med. 315:1575-1578; Thomson, 1987, Lancet 1:539-541 Kiyosawa et al., 1983, in: Zuckerman, ed., Viral Hepatitis and Liver Disease, Allen K. Liss, New York pp. 895-897; Hoofnagle et al., 1985, Sem. Liv. Dis., 1985, 9:259-263.
Chronic hepatitis C is an insidious and slowly progressive disease having a significant impact on the quality of life. Despite improvement in the quality of the blood-donor pool and the recent implementation of testing of donated blood for HCV, the estimated incidence of acute infection among persons receiving transfusions is 5 to 10%. Alter et al., in: Zuckerman, ed., Viral Hepatitis and Liver Disease, Allen K. Liss, New York, 1988, pp. 537-542. Thus, of the approximately 3 million persons who receive transfusions in the United States each year, acute hepatitis C will develop in about 150,000. While many patients who contract hepatitis C will have subclinical or mild disease, approximately 50% will progress to a chronic disease state characterized by fluctuating serum transaminase abnormalities and inflammatory lesions on liver biopsy. It is estimated that cirrhosis will develop in up to about 20% of this group. Koretz et al., 1985, Gastroenterology 88:1251-1254.
Interferons are known to affect a variety of cellular functions, including DNA replication and RNA and protein synthesis, in both normal and abnormal cells. Thus, cytotoxic effects of interferon are not restricted to tumor or virus infected cells but are also manifested in normal, healthy cells as well. As a result, undesirable side effects arise during interferon therapy, particularly when high doses are required. Administration of interferon can lead to myelosuppression resulting in reduced red blood cell, white blood cell and platelet levels. Higher doses of interferon commonly give rise to flu-like symptoms (e.g., fever, fatigue, headaches and chills), gastrointestinal disorders (e.g., anorexia, nausea and diarrhea), dizziness and coughing.
Interferon alpha-2b has been shown to be safe and effective when administered subcutaneously at a dose of 3 .times.10.sup.6 international units (IU) three times a week for 24 weeks for the treatment of chronic hepatitis C. Causse et aL. 1991, Gastroenterology 101 1:497-502; Davis et al., 1989, New Eng. J. Med. 321:1501-1506; Marcellin et al., 1991, Hepatology, 13(3) :393-393. This amount and duration alleviates symptoms of hepatitis C and biochemical or histological evidence of ongoing inflammation of the liver in some patients but it also causes undesirable side effects, e.g., flu-like symptoms. Thus, thrice weekly injections place a burden on the patient and have a significant impact on the patient's quality of life.
Nieforth et al. (Clin. Pharmacol. Ther., 1996, 59:636-646) has reported a comparison of the in vivo activity of Roferon.RTM.A and a polyethylene glycol-modified Roferon.RTM.A in healthy volunteers. The results, however, suggested that the conjugates could not be administered less than twice weekly and therefore offered little therapeutic advantage over the unmodified counterpart.
U.S. Pat. application Ser. No. 08/742,305 discloses methods of administering polymer-cytokine conjugates to individuals susceptible to treatment with the cytokine, but does not disclose the method of this invention.
Polyethylene glycol modification of other proteins has also been reported. See Fuertges et al., 1990, Journal of Controlled Release 11:139-48, which reports PEG-modified asparaginase for treatment of acute lymphoblastic leukemia, PEG-adenosine diaminase (PEG-ADA) for use in ADA-deficient Severe Combined Immunodeficiency Syndrome, PEG-superoxide dismutase for reperfusion injury and PEG-uricase for treatment of hyperuricemia.
The undesirable side effects that accompany interferon alpha therapy frequently limit the therapeutic usefulness of interferon alpha treatment regimes. Thus, a need exists to maintain or improve the therapeutic benefits of such therapy while reducing or eliminating the undesirable side effects.